Infinitely variable transmission

ABSTRACT

An infinitely variable power transmission comprising an input shaft, a layshaft driven by the input shaft via internal/external gearing, a toroidal variator, and gearing and clutches which implement a low/reverse variable ratio mode and a high range variable ratio mode. An additional clutch and gearing implement an optional fixed ratio mode.

FIELD OF THE INVENTION

This invention relates to the field of automatic transmissions for motorvehicles. More particularly, the invention pertains to transmissionswhich provide a continuous range of speed ratios, including zero,between the output speed and the input speed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a transmission according to the presentinvention.

FIG. 2 is a table showing the proposed tooth numbers for the gears andsprockets of the transmission illustrated in FIG. 1.

FIG. 3 is a table showing the speeds of various elements in variousoperating conditions when the gears and sprockets have the tooth numbersshown in FIG. 2.

FIG. 4 is a table showing the state of the clutches for each operatingmode.

DETAILED DESCRIPTION OF THE INVENTION

A transmission according to the present invention is illustratedschematically in FIG. 1. Input shaft 10 is driven by the vehicle engine,preferably via a torsional isolator that smoothes out torquefluctuations due to discrete cylinder firings. Output shaft 12 drivesthe vehicle wheels, preferably via a differential.

A dual cavity toroidal variator transfers power from variator input disk26 to variator output disks 28 and 30, which are both fixed tointermediate shaft 36. The variator is capable of efficientlytransferring power at any speed ratio within its ratio range. In thepresent embodiment, the ratio range of the variator includes 2.211:1overdrive and 0.463:1 underdrive. Two sets of power rollers 32 and 34transfer power between the input disk and the output disks. The outputdisks always rotate in the opposite direction of the input disk. Theaxes about which the power rollers rotate is tilted to control the speedratio of the variator. In the condition shown in FIG. 1, the radius ofthe interface between the power roller and the input disk is greaterthan the radius of the interface between the power rollers and theoutput disks, causing the output disks to rotate at a faster speed thanthe input disk. When the power roller axes are tilted in the oppositedirection, the output disks rotate slower than the input disk.

Two varieties of toroidal variator are well known: full-toroidal andhalf-toroidal. In a full-toroidal variator, the cavity between an inputdisk and an output disk is shaped like a torus. In a half-toroidal, asillustrated in FIG. 1, only the inner portion of the torus is used. Thepresent invention is applicable with either variety of toroidalvariator.

Power is transmitted from the input shaft to the variator input disk bymeans of at least one layshaft 16. Layshaft 16 is driven by the inputshaft through internal gear 18 which meshes with external gear 20.Internal/external gear meshes are more efficient than external/externalgear meshes. Internal gear 18 must have a relatively large diameter, butthis is acceptable because it is located in the bell housing portion oftransmission case 14. Layshaft 16 drives variator input disk 26 throughexternal gears 22 and 24. A second layshaft 68, with external gears 70and 72, causes the separating forces of the gear meshes driving thevariator input disk to partially or completely counteract one another,reducing the side loads on the variator input disk and simplifying thenecessary support bearings.

A front planetary gear set drives intermediate shaft 46 at apredetermined proportion of the input shaft speed. Sun gear 38 is fixedto input shaft 10. Ring gear 40 is fixed to transmission case 14. Planetcarrier 42 is fixed to intermediate shaft 46. A set of planet gears 44is supported on planet carrier 42 and meshes with both sun gear 38 andring gear 42.

A rear planetary gear set combines the speeds of intermediate shaft 46and intermediate shaft 36. Sun gear 48 is fixed to intermediate shaft36. Planet carrier 52 is fixed to intermediate shaft 46. A set of planetgears 54 is supported on planet carrier 52 and meshes with both sun gear48 and ring gear 50. The number of teeth on the various gears areselected such that ring gear 50 is stationary for some variator speedratio within the variator's available ratio range. This variator speedratio is called the geared neutral ratio. An example of suitable toothnumbers is provided in FIG. 2. When the variator ratio is set to a moreunderdrive ratio than the geared neutral ratio, ring gear 50 rotates inthe same direction as the input shaft. Conversely, when the variatorratio is set to a more overdrive ratio than the geared neutral ratio,ring gear 50 rotates in the opposite direction as the input shaft.

Clutch 56 releasably connects ring gear 50 to output shaft 12. Clutch 56completes a power path that is suitable for reverse motion and low speedforward motion. Substantially the same result would be obtained byplacing clutch 56 is other locations within this power path. Forexample, ring gear 50 could be fixed to output shaft 12 with clutch 56replacing one of the other fixed connections, such as between inputshaft 10 and sun gear 38, between transmission case 14 and ring gear 40,between planet carrier 42 and planet carrier 52, or between intermediateshaft 36 and sun gear 48. These alternative arrangements would result indifferent relative speeds when clutch 56 is disengaged, but identicalbehavior when clutch 56 is engaged. Clutch 58 releasably connectsintermediate shaft 36 to output shaft 12. Clutch 58 is applied formoderate to high speed forward motion. The number of teeth on thevarious gears are selected such that ring gear 50 and intermediate shaft36 rotate at the same speed at a variator ratio that is close to themaximum underdrive variator ratio.

Intermediate shaft 63 is constrained to rotate at a speed proportionalto layshaft 16 and in the same direction. Chain 64 meshes with sprocket60, which is fixed to layshaft 16, and with sprocket 62, which is fixedto intermediate shaft 63. Clutch 66 releasably connects intermediateshaft 63 to output 12. These elements form a fixed ratio power pathsuitable for highway cruising because it bypasses the variator andtherefore has better mechanical efficiency. The number of teeth on thevarious gears and sprockets are selected such that intermediate shaft 63and intermediate shaft 36 rotate at the same speed at a variator ratiothat is close to the maximum overdrive variator ratio.

Clutches 56, 58, and 66 are preferably hydraulically actuated frictionclutches which transmit torque when hydraulic pressure is applied andpermit relative motion with low drag torque when the hydraulic pressureis removed. However, since the speeds of the elements may besynchronized before engaging the oncoming clutch, other types ofcouplers, such as dog clutches or switchable one way clutches, may besubstituted for some or all of these clutches.

The vehicle is prepared for launch in reverse by disengaging allclutches and setting the variator ratio slightly on the overdrive sideof the geared neutral ratio such that ring gear 50 rotates slowlybackwards. In response to driver demand, clutch 56 is gradually engaged,accelerating the vehicle in reverse. The launch is completed when thespeed of the output shaft reaches the same speed as ring gear 50 andclutch 56 is completely engaged. As the vehicle accelerates further, thevariator ratio is adjusted to obtain a target engine speed selectedbased on driving conditions.

Similarly, the vehicle is prepared for launch in forward by disengagingall clutches and setting the variator ratio slightly on the underdriveside of the geared neutral ratio such that ring gear 50 rotates slowlyforwards. In response to driver demand, clutch 56 is gradually engaged.The launch is completed when clutch 56 is completely engaged. As thevehicle accelerates further, the variator ratio is adjusted to obtain atarget engine speed.

As the vehicle continues to accelerate, a point will be reached wherethe variator ratio is near its underdrive limit. At this point, thetransmission is shifted from low mode to high mode by releasing clutch56 while engaging clutch 58. Unlike a gear change in a traditional stepratio transmission, this transition does not involve a change in thespeed ratio between the output shaft and the input shaft. Once thetransition to high mode is complete, the controller resumes adjustingvariator ratio to obtain a target engine speed.

Typically, fixed ratio gearing provides better mechanical efficiencythan power paths that include a variator. As a result, it may bepreferable to shift to the fixed ratio mode when the vehicle is cruisingat a moderately high speed. The transmission is shifted from high modeto fixed ratio mode by releasing clutch 58 while engaging clutch 66. Asshown in FIG. 3, the tooth numbers shown in FIG. 2 result in a fixedratio mode that is slightly more overdrive than the most overdrive ratioin high mode. As a result, this shift is an upshift with a very smallratio change. However, different speed ratios of the fixed ratio mode,either higher or lower, may be selected by adjusting the number of teethon sprockets 60 and 62 without departing from the inventive concept.

A shift from fixed ratio mode back to high mode is accomplished byreleasing clutch 66 while engaging clutch 58. Preferably, the shiftshould be accomplished with the variator ratio set to minimize theoverall ratio change. Similarly, a shift from high mode back to low modeis accomplished by releasing clutch 58 and engaging clutch 56.

In accordance with the provisions of the patent statutes, the structureand operation of the preferred embodiment has been described. However,it should be noted that alternate embodiments can be practiced otherwisethan as specifically illustrated and described.

1. A power transmission, comprising: an input shaft (10); a firstlayshaft (16); an internal gear (18) fixed to the input shaft; a firstexternal gear (20) fixed to the first layshaft and in continuous meshingengagement with the internal gear; a variator input disk (26); a secondexternal gear (22) fixed to the first layshaft; a third external gear(24) fixed to the variator input disk and in continuous meshingengagement with the second external gear; a first variator output disk(28); and a first set of rollers (32) in frictional contact with thevariator input disk and the first variator output disk.
 2. The powertransmission of claim 1, further comprising: a first intermediate shaft(36) fixed to the first variator output disk (28); a second variatoroutput disk (30) fixed to the first intermediate shaft; and a second setof rollers (34) in frictional contact with the variator input disk andthe second variator output disk.
 3. The power transmission of claim 2,further comprising: an output shaft (12); and a first coupler (58)releasably constraining the first intermediate shaft (36) to rotate atthe same speed as the output shaft.
 4. The power transmission of claim3, further comprising: a second intermediate shaft (46); a secondcoupler (56); and gearing connecting the input shaft (10), firstintermediate shaft (36), second intermediate shaft, output shaft (12),and second coupler such that, whenever the second coupler is engaged:the speed of the second intermediate shaft is constrained to rotate at aspeed proportional to the speed of the input shaft; and the speed of thesecond intermediate shaft is a linear combination of the speed of thefirst intermediate shaft and the speed of the output shaft.
 5. The powertransmission of claim 3, further comprising: a second intermediate shaft(46); a first sun gear (38); a first ring gear (40); a first planetcarrier (42); a first set of planet gears (44) supported on the firstplanet carrier and meshing with both the first sun gear and first ringgear; a second sun gear (48); a second ring gear (50); a second planetcarrier (52); a second set of planet gears (54) supported on the secondplanet carrier and meshing with both the second sun gear and second ringgear; and a second coupler (56) arranged such that, whenever the secondcoupler is engaged: the input shaft is drivably connected to the firstsun gear; the first ring gear is held against rotation; and the secondintermediate shaft is drivably connected to the first planet carrier;the first intermediate shaft is drivably connected to the second sungear; the output shaft is driveably connected to the second ring gear;and the second intermediate shaft is drivably connected to the secondplanet carrier.
 6. The power transmission of claim 5, wherein: the inputshaft (10) is fixed to the first sun gear (38); the first ring gear (40)is continuously held against rotation; the second intermediate shaft(46) is fixed to the first planet carrier (42) and the second planetcarrier (52); the first intermediate shaft (36) is fixed to the secondsun gear (48); and the second coupler (56) releasably connects theoutput shaft (12) to the second ring gear (50);
 7. The powertransmission of claim 3, further comprising: a third coupler (66); andgearing connecting the first layshaft (16), output shaft (12), and thirdcoupler such that the output shaft is constrained to rotate at a speedproportional to the speed of the input shaft whenever the third coupleris engaged.
 8. The power transmission of claim 7, wherein the outputshaft (12) rotates at a speed faster than the input shaft (10) wheneverthe third coupler is engaged.
 9. The power transmission of claim 7,wherein the gearing connecting the first layshaft (16), output shaft(12), and third coupler (66) comprises: a first sprocket (60) fixed tothe first layshaft; a third intermediate shaft (63); a second sprocket(62) fixed to the third intermediate shaft; and a chain (64) incontinuous meshing contact with both the first sprocket and secondsprocket.
 10. The power transmission of claim 1, further comprising: asecond layshaft (68); a fourth external gear (70) fixed to the secondlayshaft and in continuous meshing engagement with the internal gear(18); a fifth external gear (72) fixed to the second layshaft and incontinuous meshing engagement with the third external gear (24);
 11. Apower transmission, comprising: an input shaft (10); a variator inputdisk (26); gearing constraining the variator input disk to rotate at aspeed proportional to the speed of the input shaft and in the oppositedirection; a first variator output disk (28); a first set of rollers(32) in frictional contact with the variator input disk and the firstvariator output disk; a first sun gear (38) fixed to the input shaft; afirst ring gear (40) held against rotation; a first planet carrier (42);and a first set of planet gears (44) supported on the first planetcarrier and meshing with both the first sun gear and first ring gear.12. The power transmission of claim 11, further comprising: a firstintermediate shaft (36) fixed to the first variator output disk (28); asecond variator output disk (30) fixed to the first intermediate shaft;and a second set of rollers (34) in frictional contact with the variatorinput disk and the second variator output disk.
 13. The powertransmission of claim 12, further comprising: an output shaft (12); asecond intermediate shaft (46) fixed to the first planet carrier (42); asecond sun gear (48); a second ring gear (50); a second planet carrier(52); a second set of planet gears (54) supported on the second planetcarrier and meshing with both the second sun gear and second ring gear;and a first coupler (56) arranged such that, whenever the first coupleris engaged: the first intermediate shaft (36) is drivably connected tothe second sun gear; the output shaft is driveably connected to thesecond ring gear; the second intermediate shaft is drivably connected tothe second planet carrier.
 14. The power transmission of claim 13,wherein: the first intermediate shaft (36) is fixed to the second sungear (48); the second intermediate shaft (46) is fixed to the secondplanet carrier (52); and the first coupler (56) releasably connects theoutput shaft (12) to the second ring gear (50);
 15. The powertransmission of claim 13, further comprising a second coupler (58)releasably constraining the first intermediate shaft (36) and the outputshaft (12) to rotate at the same speed.
 16. The power transmission ofclaim 12, further comprising: a layshaft (16); an internal gear (18)fixed to the input shaft (10); a first external gear (20) fixed to thelayshaft and in continuous meshing engagement with the internal gear; asecond external gear (22) fixed to the layshaft; and a third externalgear (24) fixed to the variator input disk (26) and in continuousmeshing engagement with the second external gear.
 17. The powertransmission of claim 13, further comprising: a third coupler (66); andgearing connecting the input shaft (10), output shaft (12), and thirdcoupler such that the output shaft is constrained to rotate at a speedproportional to the speed of the input shaft whenever the third coupleris engaged.
 18. The power transmission of claim 17, wherein the outputshaft (12) rotates at a speed faster than the input shaft (10) wheneverthe third coupler is engaged.
 19. A vehicle, comprising: an engine; atransmission input shaft (10) driven by the engine; a set of wheels; atransmission output shaft (12) driveably connected to the wheels; afirst layshaft (16); an internal gear (18) fixed to the input shaft; afirst external gear (20) fixed to the first layshaft and in continuousmeshing engagement with the internal gear; a variator input disk (26); asecond external gear (22) fixed to the first layshaft; a third externalgear (24) fixed to the variator input disk and in continuous meshingengagement with the second external gear; a first variator output disk(28); and a first set of rollers (32) in frictional contact with thevariator input disk and the first variator output disk.
 20. The vehicleof claim 19, further comprising: a first sun gear (38) fixed to theinput shaft (10); a first ring gear (40) held against rotation; a firstplanet carrier (42); and a first set of planet gears (44) supported onthe first planet carrier and meshing with both the first sun gear andfirst ring gear.